The renal or Malpighian tubules (MpTs) are the major excretory organs of insects. <i>Drosophila </i>has 4 MpTs, an anterior and posterior pair. During embryogenesis these MpTs undergo a morphogenetic programme such that cell rearrangement by convergent extension causes the MpTs to elongate so the short fat tubules become longer thin tubules. In addition directed migration or pathfinding occurs that the MpTs take up a specific location within the body cavity. In this study an analysis of wild type development demonstrates that several aspects of normal MpT morphogenesis are invariant whilst other aspects are less defined. The shape of an organ is a consequence of both extrinsic factors and intrinsic properties. I demonstrate that external tissues and other regulators are controlling morphogenesis of the MpTs through alterations in the cytoskeleton. I find that when the visceral mesoderm is disrupted genetically the MpTs have an aberrant morphology; the visceral mesoderm acts as an extrinsic cue for normal MpT pathfinding. The visceral mesoderm secretes Decapentaplegic (Dpp) and my analysis suggests that Dpp is an attractant controlling the normal MpT migratory behaviour. Downstream activators of the <i>dpp</i> signalling pathway are present in the MpTs and ectopic expression of Dpp in tissues near the extending MpTs affects their morphogenesis. The convergent extension process itself may be intrinsic to the MpTs and can be disrupted when signalling via the Rho family of small GTPases is perturbed. In order to identify novel genes involved in MpT morphogenesis I have analysed lines from a mutagenesis screen previously performed to select for MpT defects. One locus was mapped and characterised as an allele of <i>D-Cbl</i>, previously shown to be in inhibitor of the EGF pathway. I present evidence to show that when the regulation of EGF signalling is disrupted subtle defects on MpT morphology are observed, thus revealing a requirement for the activity of this pathway during MpT morphogenesis.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:604211 |
| Date | January 2005 |
| Creators | Hooley, Clare Verity |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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